The present invention relates to method and apparatus for filtering contaminated hydrocarbon fuels for use in diesel engines.
The problems associated with the various types of contamination found in diesel fuel have been recognized for many years. The common types of fuel contamination encountered are (1) suspended solids (2) emulsified and entrained water and (3) anaerobic bacteria. These types of contaminants are particularly harmful in diesel engines because of the fuel injection systems used to spray the fuel into the engine cylinders to facilitate combustion. The fuel injectors associated with such systems have very fine openings which may be clogged and adversely affected by such impurities.
Water presents a particularly severe problem because it not only clogs injectors but also promotes the growth of anaerobic iron bacteria that digest fuel, releasing by-products of sulfur radicals, which attack ferrous fuel tank materials and add to the particulate contamination. These various types of contamination are likely to be introduced into the diesel fuel at any time during its storage, handling and shipping prior to its being used in an engine. Ballast water on ships is a major source of contamination of fuel. The major problem created from ballast water in connection with the fuel supply for diesel engines on ships involves the filling of empty fuel tanks with ballast water. This practice is common and results in the presence of significant amounts of water-contaminated fuel. Even though the ballast water is discharged before a ship is refueled, it is well known that significant amounts of water remain in the fuel tanks and that such water mixes with the fuel and is supplied to the ship's engines. Accordingly, to be effective in solving the problem of fuel contamination particularly in marine applications, any treatment of the fuel to overcome the problem should take place as close as possible to the time when the fuel is to be used.
As a consequence of and in recognition of the fact that diesel fuels may be expected to contain a significant level of contamination of the types noted above, it has been necessary to design the fuel injection systems for diesel engines so that the injectors will accept a certain level of contamination without becoming clogged or malfunctioning. This design approach results in the use of passages and orifices in the injectors which are larger than might be desired to provide the most favorable fuel spray for complete combustion of the fuel. Accordingly, if it were possible to assure contaminate-free fuel for use in a diesel engine, that engine could be designed with more efficient fuel injection than are currently in use on diesel engines.
It is known in the filter art to construct ultrafiltration systems using semipermeable membranes configured as spiral filters to provide increased membrane filter area in a very compact form. The United States Pat. No. 4,072,610 to Gow, et. al. is of interest with respect to the present invention in disclosing a filtering system utilizing spiral-wound membrane filters with a failure alarm associated with a particulate filter element. Of similar interest are the U.S. Pat. Nos. 4,784,763 to Hambleton, et. al. and 4,534,865 to Sundberg, et. al.
In the field of filtering, it is known that there are semipermeable membranes that are effective in selectively filtering small particles, water, bacteria and the like, and through selection of appropriate membrane materials and pore sizes in such membranes, it is known to purify liquids by filtering out contaminants However, in spite of there being known membranes that could be used in filtering such liquids as diesel fuel to remove these contaminants, there are no adequate systems for use with a diesel engine to purify the fuel and to assure that fuel 100% free of the various contaminants described above is continuously supplied. Prior art filtering systems that have alarm systems responsive to a breakthrough in the filter membranes have no backup means to guarantee that shutdown of the system will occur prior to some of the impurities being allowed to pass through the system and cause malfunctioning in the device for which the filtrate is to be supplied. If the device is a diesel engine, the passage of limited amounts of impurities to the engine may result in serious malfunctioning problems in connection with the fuel injectors. Accordingly, it is important that the system be such that during the period of breakthrough until the supply system is interrupted there should be means to prevent delivery of impurities and contaminants to the engine.